The transmitting device is intended to transmit energy and/or information to the electronic device, which may be a sensor, a counter or a device fulfilling another function. The sensor may, in particular, be a force sensor, a temperature sensor or a pressure sensor. The electronic device is intended, as applicable, to communicate data, for example signals relating to measurements, counting or the like, to the transmitting device.
The electronic device is therefore connected to at least a first so-called receiving inductive antenna which must be coupled electromagnetically with at least a second so-called transmitting inductive antenna of the transmitting device. This transmitting device will supply energy to the electronic device and/or control its operation and, where applicable, retrieve the data which it supplies to it. The two antennae are each formed from a conductor in a loop arranged in one or more turns. The two antennae will communicate all around a working frequency ν. The principle is to generate, from the transmitting device, an electromagnetic field at the working frequency ν by means of which energy and/or information will be transmitted.
The energy is transmitted by the carrier wave and is a function of the amplitude of the latter.
The transmitting device comprises, in addition to the transmitting antenna, electronic means for generating the working frequency ν and a modulation stage in order to be able to transmit the information in electromagnetic form all around the working frequency to the electronic device. The information is transmitted by the modulation of this same carrier, which may be amplitude, frequency or phase modulation.
The transmitting device can also comprise means for processing the data received from the device.
The receiving device for its part comprises, cooperating with the electronic device, an electronic circuit, this circuit being able to be a rectifying circuit.
French Patent publication FR-A1-2 771 965 describes a tire provided with a receiving antenna connected to a sensor. The antenna and sensor are located in the tire. The antenna is intended to be coupled electromagnetically with another antenna situated outside the tire. The rectangular-shaped receiving antenna, when it is put flat, extends along the periphery of the tire under its tread between a sealing layer (also referred to as the inner liner), situated on the same side as the internal face of the tire, and the radial carcass reinforcement.
The working frequency ν is an important parameter since it determines the characteristics of the receiving antenna of the receiving device and those of the transmitting antenna of the transmitting device. The receiving antenna has a resonant frequency which is a function of its intrinsic characteristics, that is to say the resistance of its conductor, the length of its conductor, the value of the intrinsic capacitance distributed along its conductor, its surface area and external characteristics related to its environment such as the magnitude of the stray capacitances and the propensity of the environment to channel the magnetic field lines.
In order to function optimally the receiving antenna of the receiving device must be tuned to the working frequency ν. The tuning is carried out normally by means of a tuning capacitor connected in parallel with the antenna. On tuning, the following equation is satisfied:
LC(2πν)2=1 with L the inductance of the receiving antenna, C the total capacitance of the receiving antenna. These quantities L and C are quantities equivalent to the working frequency seen by the receiving device. For example, C will be the sum of all the capacitances involved at the receiving antenna: the intrinsic capacitance of the antenna, the stray capacitance and the capacitance of the tuning capacitor.
Among working frequencies permitted by the AFNOR standards and which correspond to the ISM bands, a working frequency of around ten megahertz is chosen, since with a higher frequency it would be difficult to transmit energy and with a lower frequency the information flow rate would be too low. Having regard to this working frequency, the low power levels involved during the transmission with the transmitting device, the ambient noise and the small size imposed on the transmitting device, which is situated on the vehicle on which the tire is mounted, the surface area of the receiving antenna of the receiving device is large compared with that of the transmitting antenna of the transmitting device.
This results in a resonant frequency that is lower than the working frequency ν, a high inductance and a high intrinsic capacitance distributed along the conductor and seen by the electronic device. In the tire, high stray capacitances may exist close to the antenna. These are due to the elastomers with a carbon black or silica filler, which are the main constituents of the tire, and to the structure of the tire comprising metallic reinforcements on a crown, and in certain cases a carcass reinforcement which is also metallic.
A long narrow antenna shape also results in a reduction in the resonant frequency.
If the resonant frequency of the receiving antenna is too low vis-à-vis the working frequency ν, it is not possible to tune the receiving antenna of the receiving device to the working frequency ν since the value of its intrinsic capacitance is already too high to achieve tuning. Adding a tuning capacitor would aggravate the situation still further. If tuning is not achieved, the coupling between the receiving antenna and the transmitting antenna cannot be optimum and the transmission efficiency is not good. Nor can reducing the surface area of the receiving antenna in order to attempt to achieve tuning be envisaged, since this would impair the quality of the coupling.
There is a risk that the receiving antenna described in French patent publication FR-A1-2 771 965 might, because of its location, not be coupled correctly to the transmitting antenna external to the tire. This is because, with respect to the outside of the tire, it is situated under the carcass reinforcement, which is electrically conductive and will then have the role of a Faraday cage.
The present invention aims to mitigate the drawbacks mentioned above and in particular aims to improve the tuning between a receiving antenna with which a tire is provided and a transmitting antenna situated outside the tire, for example on a vehicle equipped with a tire, without having to reduce the surface area of the receiving antenna connected to the electronic device or having to reduce the working frequency.
More precisely, the present invention proposes a tire equipped with at least one receiving antenna of a receiving device which includes an electronic device intended to be remote controlled by electromagnetic coupling with at least one transmitting antenna. This receiving antenna is intended to be connected to the electronic device and is divided into several loop parts arranged in a parallel circuit, these loop parts each having a surface, these surfaces being juxtaposed overall so that the loop parts can be coupled successively and continuously to the transmitting antenna.
In the context of the present invention, the term “tire” applies not only to the casing inflated at a certain nominal pressure for its normal operation, but also a non-pneumatic elastic casing. “Tire” therefore designates in general terms any product equipped with a tread which runs on the roadway.
The receiving antenna has a useful surface for reception with the transmitting antenna and the sum of the surfaces of all the loop parts is substantially equal to the useful surface of the receiving antenna. With such a structure, the surface of the receiving antenna can advantageously be much larger than that of the transmitting antenna.
To provide good coupling with the transmitting antenna, it is preferable, the loop parts being formed by a conductor, for a portion of a conductor of a first loop part and a portion of a conductor of a second loop part, adjacent to the first loop part, to be separated by a space which is as small as possible.
In the same way, it is preferable for the loop parts to be separated, on the electronic device side, by a space which is as small as possible.
To facilitate tuning between the transmitting antenna and the receiving antenna, a tuning capacitor can be connected in parallel with at least one of the loop parts. The antenna is advantageously shielded in order to reduce its electrical radiation, in particular close to the electronic device and/or the electronic circuit.
The receiving antenna can be immobilized between two sheets of an electrically insulating material in order to form a complex which is installed in the tire.
The tire can comprise, in a crown area, at least one crown reinforcement surrounded by a tread, the complex being inserted between the crown reinforcement and the tread.
It is preferable to produce the sheets of the complex from a material having mechanical properties close to those of the tread so that the insertion of the receiving antenna interferes with the behavior of the tire to the minimum extent.
In another embodiment, the tire comprising a carcass reinforcement covered towards the outside with an external sidewall, the complex can be inserted between the carcass reinforcement and the external sidewall.
The sheets of the complex can be produced from an elastomer with silica and carbon black fillers, this material having a low carbon black content so as to leave it electrically insulating.
It is advantageous, particularly from the point of view of cost and adhesion to the rubber compound, to produce the loop parts with a bare metallic conductor. This conductor can comprise one or more wires.
It is possible to produce the conductor with one or more wires which are of the same nature as the reinforcement wires conventionally employed in the tire. These may be steel wires brass-coated on the surface, or any other wire or cable treated or coated in an appropriate fashion for bonding directly to the rubber.
It is preferable for the conductor to be undulated with a wave pitch adapted to the deformations existing at the point chosen for the installation of the antenna, so as not to interfere with the mechanics of the tire during running.
The conductor can be glued to at least one of the sheets of the complex in order to guarantee good strength of the complex over time.
The tire can be equipped with the electronic device. The electronic device can cooperate with an electronic circuit with which the tire is also equipped.
The electronic circuit can comprise a single rectifying circuit, the loop parts having at least one end connected to the input of the rectifying circuit, the electronic device being connected to the output of the rectifying circuit.
In a variant, the electronic circuit can comprise several rectifying circuits, each loop part having at least one end connected to the input of one of the rectifying circuits, the rectifying circuits having their outputs connected in series with the electronic device.
The electronic device and/or the electronic circuit can be located in a crown area of the tire.
In another embodiment, the electronic device and/or the electronic circuit can be located in a sidewall of the tire.
In yet another embodiment, the electronic device and/or the electronic circuit can be located in an internal volume defined by the tire.
The electronic device and/or the electronic circuit can be located in the complex.
The electronic device can be a sensor, a counter or an electronic label.
The electronic device and/or the electronic circuit can advantageously be shielded in terms of electrical field.
The present invention also concerns a method of producing a tire comprising the following steps:
preparing a carcass,
preparing a complex comprising a receiving antenna divided into several loop parts arranged in a parallel circuit, the receiving antenna being secured between two sheets of an electrically insulating material, preferably made from non-vulcanized elastomer material, compatible with the normal materials of the tire,
providing a connection with at least one electronic device intended to be remote controlled by electromagnetic coupling between the receiving antenna and at least one transmitting antenna,
installing the complex on the tire,
covering the complex with an elastomer with a filler and finishing so as to obtain an uncured tire,
molding and vulcanizing the uncured tire.
The elastomer with filler forms a tread of the tire or contributes to forming a sidewall of the tire depending on whether the antenna is situated in the sidewall or in the crown.
The method can comprise a step of replacing at least one crown reinforcement on the carcass before positioning the complex.
The method can also comprise a step of forming in the carcass a hole opening out in an internal volume delimited by the tire, this hole being intended to contain connection conductors for the connection between the receiving antenna and the electronic device, the electronic device being situated in the internal volume. This step is followed by a step of replugging the drilled hole containing the conductors through the inside of the tire before curing.
The step of preparing the complex can include the production of at least one extension or flap in which connection conductors are immobilized for the connection between the receiving antenna and the electronic device, this extension being folded over a sidewall of the tire when the complex is placed on a crown area of the tire or on the crown area when the complex is placed on the sidewall.